Transnistria (also called Trans-Dniestr or Transdniestria) is a breakaway state located mostly on a strip of land between the River Dniester and the eastern Moldovan border with Ukraine. Since its declaration of independence in 1990, and especially after the War of Transnistria in 1992, it is governed as the Pridnestrovian Moldavian Republic (PMR, also known as Pridnestrovie) a state with limited recognition that claims territory to the east of the River Dniester, and also to the city of Bender and its surrounding localities located on the west bank, in the historical region of Bessarabia. The terms "Transnistria" and "Pridnestrovie" both reference the Dniester River.

Unrecognised by any United Nations member state, Transnistria is designated by the Republic of Moldova as the Transnistria autonomous territorial unit with special legal status , or Stînga Nistrului ("Left Bank of the Dniester").

After the dissolution of the USSR, tensions between the newly created Moldova and the de facto sovereign state of Pridnestrovia (which unlike the rest of Moldova had not wanted to separate from the Soviet Union), escalated into a military conflict that started in March 1992 and was concluded by a ceasefire in July 1992. As part of that agreement, a three-party (Russia, Moldova, Transnistria) Joint Control Commission supervises the security arrangements in the demilitarized zone, comprising twenty localities on both sides of the river. Although the ceasefire has held, the territory's political status remains unresolved: Transnistria is an unrecognized but independent presidential republic with its own government, parliament, military, police, postal system, and currency. Its authorities have adopted a constitution, flag, national anthem, and coat of arms. However, after a 2005 agreement between Moldova and Ukraine, all Transnistrian companies that seek to export goods through the Ukrainian border must be registered with the Moldovan authorities. This agreement was implemented after the European Union Border Assistance Mission to Moldova and Ukraine (EUBAM) started its activity in 2005. Most Transnistrians also have Moldovan citizenship, but many Transnistrians also have Russian and Ukrainian citizenship.

Because of the Russian military contingent present in Transnistria, the European Court of Human Rights considers Transnistria "under the effective authority or at least decisive influence of Russia".

Transnistria, Nagorno-Karabakh, Abkhazia, and South Ossetia are post-Soviet "frozen conflict" zones. These four unrecognized states maintain friendly relations with each other and form the Community for Democracy and Rights of Nations.